Cell structure and organization

Chloroplasts

o Site of photosynthesis where light energy is absorbed

o Consist of grana which are stacked up to increase surface area for absorption

of light

o Only present in plant cells

Cell membrane (plasma membrane)

o Lipid bilayer that surrounds the cell, interspersed with protein molecule

o Presence of temporary pores

o Selectively permeable

Controls movement of substances

o Diffusion, osmosis and active transport can therefore take place

o Prevent outflowing of cytoplasm

o Tonoplast

Plasma membrane surrounding the vacuole

Cell wall

o Made of cellulose (a polysaccharide), and may be deposited with ligin

o Maintain cell turgidity, provide mechanical support, protect from mechanical

damage

o Freely permeable to water and most solutes

o Only present in plant cells

Cytoplasm

o Protoplasm surrounding the nucleus

o There are numerous organelles present in the cytoplasm

o Organelle

Specialized membrane bound structures

Cell vacuole

o Fluid-filled space enclosed by a membrane

o In animal cells, these are present as numerous small ones, and these are

usually not permanent

o In plant cells, there is usually a large central vacuole

o Cell sap

Fluid in vacuoles, contains sugars, mineral salts and amino acids

o Tonoplast

Membrane around the vacuole

Nucleus

o Nucleoplasm

Small spherical mass of denser protoplasm

o Nuclear membrane

Nuclear envelope

o Found in the cytoplasm

o Control activities of the cell

Reproduction, repairs and maintenance

o Chromatin

Network of long thread-like structures, containing the heredity

materials

o Chromatin is made up of proteins and DNA (Deoxyribose Nucleic Acid)

o Chromosomes

Condensed and highly coiled chromatin threads during cell division

o Nucleoli

A spherical structure that plays a part in the build up of proteins

Endoplasmic reticulum

o A series of flattened sheets

o Smooth endoplasmic reticulum

Sites of synthesis and transport of steroids and lipids

o Rough endoplasmic reticulum

Transport proteins synthesized at the ribosomes towards Golgi bodies

for secretary packing

Mitochondria

o Rod-shaped

o Site of aerobic respiration

o Powerhouse

Release energy during cellular respiration

Golgi bodies

o Stacks of flattened membrane sacs

o Involved in secretion of vesicles, formation of lysosomes

Ribosomes

o Tiny structures concerned with the manufacture of proteins

o Found on rough endoplasmic reticulum

Comparison between plant cell and animal cell

Plant cell Animal cell

Cell wall √ X

Cell membrane √ √

Chloroplasts √ X

Mitochondria √ √

Golgi apparatus √ √

Endoplasmic reticulum √ √

Nucleus √ √

Shape Fixed Irregular

Centriole X √

Vacuoles One large central Many small

Granules Starch Glycogen

Cilia/flagella X √

o All cells have cell membrane, cytoplasm, nucleus, mitochondria, endoplasmic

reticulum and ribosomes

Root hair cell

o Function

Increase absorption of water and mineral salts from the soil

o Presence of root hair

o Long and elongated

o Increase surface area for greater rate of absorption

Xylem vessel

o Function

Conduction of water in plants as well as to offer mechanical support

o Narrow and cylindrical continuous tube

o Absence of cross wall

o Water column can move easily up the lumen of the xylem vessel

o Lignified cell walls

o Strengthens the wall and prevents collapse of the xylem vessel

Red blood cell

o Function

Transport of oxygen from lungs to the rest of the body

o Contains hemoglobin

Oxygen carrier

o Flat, biconcave shape (no nucleus)

o This serves to increase surface area to volume ratio

o Oxygen can also diffuse into or out of the cell at a faster rate

o The absence of a nucleus also allow the red blood cell to squeeze through the

narrow capillaries

Cell

o Basic structural unit of all organisms

o Functional unit of all organisms where all chemical reactions necessary to

maintain and reproduce the living system exist

o Arise from pre-existing cells

o Contain heredity material

Simple tissue

o Cells of the same type grouped together to carry out special function

Complex tissue

o Cells of different type grouped together for the same function

Organ

o Different tissues working together and enabling the organ to perform its

function

Organ system

o Different organs working together for a special purpose

Movement of substances

Diffusion

o The random movement of molecules of a substance from a region of higher

concentration to a region of lower concentration

Osmosis

o The movement of water (or solvent) molecules from a region of higher

concentration to a region of lower concentration across a partially permeable

membrane

Active transport

o The movement of substances into or out of cells against a concentration

gradient

Water potential

o The measure of the free kinetic energy of water in a system, or the tendency

for water to leave a system

o High water potential = high tendency for water to leave the system/low

tendency for water to enter a system/high concentration of water

Osmotic potential

o Low osmotic potential = low tendency for water to enter a system/high

tendency for water to leave the system/high water potential/high

concentration of water

Hypertonic environment

o Cell has high water potential

o Cell has low osmotic potential

o Water leaves the cell

Hypotonic environment

o Cell has low water potential

o Cell has high osmotic potential

o Water enters the cell

Isotonic solution

o Cell gains and lose water at the same rate

o No net loss or gain in water

Biological molecules

Importance of water

o Use as a biological solvent

Medium where chemical reactions occur

o As a reagent in the digestion or hydrolysis of food

o As a transport medium for digested food like glucose, amino acids in animals

o As a transport medium for wastes like CO2, urea and other nitrogenous

wastes like creatinine in animals

o As a transport medium for hormones from the glands to the target organs

o For heat loss since water has a high specific heat capacity

o As a major component of body fluids such as blood, tissue fluid and digestive

juices

o Replaces water lost from the body in sweat, urine and in breath

o Act as a lubricant in mucus and synovial fluid

o Essential constituent of protoplasm

o Essential for photosynthesis in green plants

o Maintains turgidity of plant cells and to keep plants upright

o Transport medium for mineral salts and manufactured sugars in plants

Carbohydrates

o Chemical constituents

Carbon

Hydrogen

Oxygen

Fats

o Chemical constituents

Carbon

Hydrogen

Oxygen

Proteins

o Chemical constituents

Carbon

Hydrogen

Oxygen

Nitrogen

o Other possible constituents

Sulfur

Phosphorus

Starch test

o Drops of iodine

Blue-black color if starch is present

Brown color if starch is present

Reducing sugars test

o Benedict’s solution

Green color mixture means traces of reducing sugars

Yellow or orange color precipitate means moderate amounts of

reducing sugars

Brick-red or orange-red color precipitate means large amount of

reducing sugars

Protein test

o Biuret solution

Sodium hydroxide

Copper (II) sulfate

o Color change

Blue to violet (proteins)

Blue to pink (short-chain polypetides)

Fat test

o Ethanol

o Water

o Observation

Cloudy white emulsion if fats are present

Synthesis

o Glycogen from glucose

o Polypetides and proteins from amino acids

o Lipids such as fats from glycerol and fatty acids

Enzymes

o Lock and key

Highly specific

Only substrates with shapes complementary in shape to that of the

enzymes can fit into the enzyme active site and be acted upon by the

enzymes

o Active site

Site with a specific shape where substrate will bind onto enzyme

o Enzyme-substrate complex

Formed only long enough for the reaction to be complete

Same enzyme molecule can then catalyze the reaction with another

substrate molecule

o Activation energy

Reduces activation energy so that it is possible for chemical reactions

to take place in cells at normal body temperature

o Enzyme specificity

Only substrates with shapes complementary to that of the enzyme can

fit into enzyme active site and be acted upon by the enzyme

o Effects of temperature

Enzymes have an optimum working temperature often but not always

close to that at which they usually function

An enzyme is inactive at low temperatures

This is because enzyme-substrate complexes are formed slowly

As temperature rises, it activity increases

The rising temperature increases the rate of metabolic reactions as the

heat increases molecular motion

Thus the molecules move more quickly and frequency of collision

between substrate and enzyme molecules increases

Hence, there is a greater possibility of a reaction taking place

Q10

The rate of reaction double for every 10°C rise in temperature

until optimum temperature is reached

The temperature coefficient Q10 varies between enzymes,

depending on the activation energy of the catalyzed reaction

Optimum temperature

The temperature at which maximum reaction occurs

Beyond optimum temperature, enzyme activity will decrease

until it is completely deactivated or destroyed

As enzymes are made of proteins, when they are heated to too

high a temperature, they are denatured

Denaturation

The breaking of the secondary tertiary structures of

proteins/enzymes due to high temperatures

An irreversible (≈60°C) destruction of an enzyme can be

brought about by extreme heating

Each enzyme has its own optimum temperature

Most enzymes work best between 30-37°C

Enzymes in the human body have an optimum temperature of

37°C

o Effects of pH

Extreme changes in pH of the solutions destroy the enzymes

Optimum pH

The pH at which the maximum rate of reaction occurs

When the pH is altered above or below the optimum pH, the

rate of enzyme activity decreases as changes in pH alter the

ionic charge of the acidic and the basic groups that help

maintain the specific shape of the enzyme

pH changes lead to alterations in enzyme, particularly at the

active site

extreme pH changes can cause denaturation of the enzyme

Animal nutrition

Digestion

o Mouth

The presence of food in the mouth or thoughts of food stimulates the

three pairs of salivary glands to secrete saliva

Food is mixed with saliva and is softened by mucin

Mastication breaks down food into smaller pieces (increase in surface

area/physical digestion)

The enzyme amylase, present in saliva, digests starch to maltose

Bolus

Small, spherical mass of food formed by mastication and the

rolling of the tongue

Bolus is swallowed via the pharynx into the esophagus

o Esophagus

Bolus passes down the esophagus into the stomach through gravity as

well as peristalsis

No digestion takes place in the esophagus

o Stomach

Food in the stomach stimulates the secretion of gastric juices into the

stomach cavity by the gastric glands

Peristaltic movement in the stomach churns the food and mixes it well

with gastric juice (as well as to break down the food substances into

smaller pieces)

Gastric juice

A dilute hydrochloric acid (≈pH 2), prorenin and pepsinogen

The functions of hydrochloric acid

Stops action of salivary amylase

Converts inactive forms of gastric enzymes to active forms o Pepsinogen pepsin

o Prorenin rennin

Provides a slightly acidic medium for the action of digestive

enzymes

Kills germs and certain potential parasites

Excess production of hydrochloric acid may erode the stomach walls

and thus result in gastric ulcers

Pepsin causes the breakdown of proteins to peptones or polypeptides Proteins + pepsin peptones

Since pepsin breaks down proteins, these need to be formed in the

inactive state before being released, otherwise they will breakdown the

proteins found in the cells that produces them

Renin is an enzyme characteristic of mammals

Renin clots or curdles milk proteins by converting the soluble protein

caseinogen into insoluble casein, a process that requires calcium ions Caseinogen (soluble) + renin/Ca2+ casein (insoluble)

The insoluble casein would remain long enough in the stomach to be

digested by pepsin

Protein digestion would be completed in the ileum

Food normally remains in the stomach for about three to four hours

Chyme

Liquefied, partly digested food that passes in small amounts

into the duodenum through the pyloric sphincter

Small intestine

The presence of chyme stimulates

Secretion of intestinal juice (succus entericus (which contains

enzymes enterokinase), erepsin (peptidase), maltase, sucrase

(or invertase), lactase and intestinal lipase by the intestinal

glands)

Secretion of pancreatic juice (pancreatic amylase, pancreatic

lipase, trypsinogen, an inactive form of protease) by the

pancreas into the duodenum

Release of bile by the gall bladder into the duodenum

Acidic chyme comes into contact with intestinal juice, pancreatic juice

and bile and is neutralized

An alkaline environment is now created to provide a suitable alkaline

medium for the action of pancreatic and intestinal enzymes

Carbohydrate digestion in small intestine

Digestion of starch in the mouth is minimal

Also, there is no digestion of starch in the stomach

Remaining starch that enters the small intestine are digested

by pancreatic amylase to maltose, then to glucose by maltase

Simple sugars are the end-products of carbohydrates digestion

Fat digestion in small intestine

Bile emulsifies fat by breaking fats up into minute fat globules

suspended in water to form a stable emulsion

Emulsification increases the surface area of fats for digestion

Digestion of fats sped up

Emulsified fats are converted by lipases to fatty acid and

glycerol

Protein digestion in small intestine

Some protein digestion occurs in the stomach

Undigested proteins in the small intestine are converted by

trypsin to peptones, which are converted erepsin to amino acids o Trypsinogen + enterokinase trypsin

o Proteins + trypsin peptones

o Peptones + erepsin amino acids

Absorption

o Digested food substances are absorbed by the villi of the small intestine,

especially in the jejunum and ileum

o The wall of the small intestine is well adapted for the absorption of digested

food substances

Inner walls of the small intestine thrown into many transverse folds

and furrows

Villi

Minute finger-like projections found on the wall of the small

intestine

Numerous villi are found on the folds and furrows of the small intestine

Microvilli

Minute finger-like projections found on villi

The presence of folds and furrows, as well as villi and microvilli, serve

to increase surface area for absorption

The long length of the small intestine also increases surface area for

absorption to take place

The epithelium is only one cell thick

The intestinal wall and the villi are richly supplied with blood vessels

and lymphatic vessels

The presence of these vessels serve to carry away digested food

substances

Lacteal

A lymphatic vessel present in a villi which is surrounded by

blood capillaries

Aid in the transport of fat

Blood vessels carry sugars and amino acids

This continuous transportation of digested materials away aids to

maintain concentration gradient

Process

Simple sugars and amino acids, since they are relatively small

in size, diffuse through the walls of the villi into the blood

capillaries

Mineral salts and vitamins, since they are relatively small in

size, also diffuse through the walls of the villi into the blood

capillaries

Transport of digested food substances into the blood capillaries

can be through diffusion or by active transport

Fats are broken down into glycerol and fatty acids

o Glycerol is soluble in water and it diffuses through the

epithelium

o Fatty acids reacts with bile salts to form soluble soaps so

that it can diffuse through the epithelium

o In the epithelium, glycerol and the soluble soaps

recombine to form minute fat globules which are

absorbed by the lacteals

Water and mineral salts are also absorbed by the large

intestines

The epithelium layer of the villi is one cell thick

o This allows digested food substances to diffuse rapidly

over a short distance into the blood capillaries or lacteal

Undigested food substances and unabsorbed digested matter

are stored temporarily in the rectum before being discharged as

feces through the anus

Egestion

o Removal undigested matter from the body

Transportation and utilization of absorbed foods

o Sugars

Blood capillaries in the villi unite to form a large vein, the hepatic

portal vein

The hepatic portal vein is linked to the liver

Simple sugars are transported to the liver, where most of these are

converted to glycogen and stored

Conversion of glucose to glycogen is carried out in the presence of the

hormone insulin, produced by the pancreas

Glucose + insulin (from pancreas) glycogen

The unconverted sugars are transported to the other parts of the body

as glucose for assimilation

Glucose is needed for cellular respiration

Hence, when the body is in need of glucose, glycogen is converted

back into glucose in the liver and transported away to other parts of

the body

The conversion of glycogen to glucose is under the action of the

hormone adrenaline Glycogen + glucagon (from pancreas) glucose

o Amino acids

The route of transport for amino acids is similar to that of simple

sugars (after being transported to the liver, it is transported in the

blood stream to other parts of the body)

Amino acids are assimilated for

New protoplasm

Growth and repair

Formation of hormones

Formation of enzymes

Excess amino acids not utilized are brought back to the liver

Deamination

Removal of the amino groups (-NH2) and conversion into

ammonia, then urea of excess amino acids

Urea is transported to the kidneys to be removed in the urine

The remains of amino acids are converted into glucose (and then to

glycogen) in the liver

o Fats

Lymph

A colorless fluid in lacteals

Chyle

Milky fluid obtained when fats in the lacteals are mixed with

lymph

Lacteals linked together into larger lymphatic vessels, discharging into

the thoracic duct, and ultimately opening into the subclavian vein

Fats are then carried to the liver and assimilated

When there is an inadequate supply of glucose, the fats are oxidized to

provide energy

Under normal conditions, fats are used to build protoplasm

Excess fats are stored in adipose tissues

Adipose tissues

A layer of tissues beneath the skin, around the heart, the

kidneys and in the mesenteries binding the intestines, where

fats are stored

Peristalsis

o Rhythmic, wave-like contractions of the alimentary canal wall to move food

along the alimentary canal

o Brought about by the antagonistic actions of the circular and longitudinal

muscles

Dilation

Circular muscles relax, longitudinal muscles contract

Constriction

Circular muscles contract, longitudinal muscles relax

Functions of liver

o Carbohydrate metabolism

Glycogen is converted to glucose in the liver in the presence of

glucagon from the pancreas

o Fat metabolism

Lipids are removed from the blood and broken down

E.g. cholesterol is excreted in the bile

o Breakdown of red blood cells

The red blood cells become worn out after a period of time and are

destroyed by the spleen

The hemoglobin of red blood cells are brought back to the liver where

it is broken down and the iron released is stored

Bile pigments are formed from the breakdown of hemoglobin

o Metabolism of amino acids and the formation of urea

The amino group is converted into urea and is removed from the body

in the urine

The remains of the deaminated amino acids are converted to glucose

in urea

Plant nutrition

Adaptations of dicotyledonous leaf

Part of the leaf Structure Function

Upper epidermis One cell thick layer

Waxy cuticle

No chlorophyll

Stomata may be present in small

numbers

Cuticle reduces loss of water

through evaporation

Cuticle also protects the leaf from

mechanical injury

The upper epidermis and the

cuticle is transparent, thus

allowing light to pass through

easily

Palisade mesophyll Densely packed cylindrical-

shaped cells arranged at right-

angles to the upper epidermis of

the leaf in one or two layers

Cells have thin walls and contain

many chloroplasts

Palisade mesophyll cells are the

main sites where photosynthesis

takes place due to high

concentration of chlorophyll

Thin cell wall and cytoplasm

allows rapid diffusion of water

and carbon dioxide into the

chloroplasts

Spongy mesophyll Irregularly-shaped cells

containing fewer chloroplasts

Cells are loosely packed with

large intercellular air spaces

Air spaces are connected with the

stomata (serves as passage way

for diffusion of carbon dioxide and

oxygen, as well as water vapor)

between cells Some photosynthesis occurs and

this causes the cells to be turgid

(support)

Vascular bundles Lignified xylem vessels and

tracheids

Phloem tissues with sieve tubes

and companion cells

Xylem aids in the conduction of

water and mineral salts from the

roots to the leaves

Provides support for the leaf

lamina

Phloem aids in transport of

products of photosynthesis from

the leaves to other parts of the

plant, especially to the roots, in

the form of sucrose

Lower epidermis One cell thick layer

Waxy cuticle

Presence of many stomata

Stomata allow gaseous exchange

between external environment

and the intercellular air spaces in

the spongy mesophyll

Stomata A pair of curved guard cells

surrounding a stomatal pore

Gaseous exchange occurs

through the stomatal pore

Opening or closure of guard cells

regulates gaseous exchange

Photosynthesis

o Equations

Word equation Carbon dioxide + water glucose + oxygen + water

Chemical equation 6CO2 + 12H2O C6H12O6 + 6O2 + 6 H2O

o Intake of carbon dioxide

Carbon dioxide from the atmosphere diffuses into the leaf through the

stomata

Once the carbon dioxide enters the leaf, it dissolves in the thin film of

water surrounding the spongy mesophyll cells and palisade mesophyll

cells and finally diffuse into the chloroplasts within the cells and used

in photosynthesis

o Effects of varying light intensity

In the absence of light, photosynthesis does not occur and only

respiration continues

As light intensity increases, the rate of photosynthesis increases until

the amount of carbon dioxide released from respiration is equal to the

amount of carbon dioxide absorbed for photosynthesis

As higher light intensities, a net uptake of carbon dioxide and release

of oxygen is reached and the amount of sugar in the plant will increase

The rate of photosynthesis increases with increasing light intensity up

to the light saturation point

Beyond the light saturation point, further increase in light intensity has

no effect on the rate of photosynthesis

At very high light intensities, the rate of photosynthesis slows down as

excessive amounts of ultraviolet rays damages chlorophyll molecules

Blue light and red light are most strongly absorbed by chlorophyll

pigments

Thus, the highest photosynthetic rate is obtained when leaves are

illuminated with blue and red light

o Effects of temperature

The reaction in dark stage of photosynthetic process are catalyzed by

enzyme

Increasing temperature up to 40°C will increase the rate of

photosynthesis due to increased enzyme activity

At temperatures above 40°C, the rate of photosynthesis slows down as

the enzymes are denatured gradually

o Effects of carbon dioxide

The normal percentage of carbon dioxide in atmospheric air is 0.03%

Increasing carbon dioxide level increases the rate of photosynthesis up

to the carbon saturation point

Further increase in carbon dioxide levels had no effect on the rate of

photosynthesis

Carbon dioxide levels of greater than 0.1% have no effect on rate of

photosynthesis

o Limiting factor

Definition

Any factor that directly affects a process if the quantity of this

factor is changed

In the case of photosynthesis

Light

Carbon dioxide concentration

Temperature

Graphs show the effect of light and carbon dioxide concentration on

photosynthesis rates

In each case, the rates increase rapidly at first, then reach a ceiling,

indicating that they are being affected by another limiting factor, for

example, temperature

For example, in the first graph, by increasing the temperature, the

rate of photosynthesis showed only a small increase

It is likely that temperature may not be an important limiting factor in

this example

In the second graph, carbon dioxide concentration is increased instead

There is a significant increase in the rate of photosynthesis

It is likely that carbon dioxide is an important limiting factor in this

example

This is true in nature as there only is 0.03% CO2 in air

Thus, carbon dioxide concentration is the limitation factor

Carbon dioxide levels can only be raised under laboratory conditions

The constant rate of photosynthesis even when carbon dioxide

concentration is raised implies that there is another limiting factor at

work

In the third graph, with raised carbon dioxide concentration,

temperature is increased

Again, there is a significant increase in the rate of photosynthesis

This shows that temperature was a limiting factor

Compensation point

At certain light intensity, the rate of photosynthesis and the

rate of respiration is equal

This means that the amount of CO2 taken in and O2 released is

the same

Transport in flowering plants

Xylem

o Functions

Conducts water and its dissolved mineral salts from the roots to the

stems

Provide mechanical support to the plant

Phloem

o Functions

Conducts manufactured nutrients (sucrose and amino acids) from the

leaves to other parts of the plant

Root

o Structure

The root consists of various regions or zones

Growing zone

Small young cells that are actively dividing to form new cells

Zone of elongation

Cells elongate here to bring about increase in length of the root

Root cap

Several layers of protective cells to protect the young cells from

injury during elongation

Zone of root hairs/maturation

Absorption of minerals and water occurs here

The region of the root about the zone of root hairs has an outer skin

which is impregnated with suberin

This allows it to be air proof as well as waterproof

o Structure of a young dicotyledonous root

Xylem and phloem are not bundled together

Cortex present as a storage tissue

Piliferous layer

Epidermal layer of the root which bears root hair cells

Root hairs serve to increase surface area to volume ratio for the

adaptation of absorbing water and mineral salts

Cuticle is missing

o Movement of water

Absorption of water and mineral salts takes place mainly in the zone of

root hairs

Root hairs increase surface area for uptake of water

Sap in root hair is a relatively concentrated solution of sugars and

various salts

Thus the sap has a lower water potential than the soil water

Water enters the root hair cells by osmosis

Cell sap and soil water is separated by a partially-permeable plasma

membrane

Entry of water dilutes the root hair cell sap

This causes water to move into the inners cell by osmosis

As water moves into these cells, they have a higher water potential

than cells further in, thus water will move in further into the roots

The process continues until the water enters the xylem vessels and

moves up the plant

o Pathway of water from root to leaves Root hair cells epidermis of root cortex of root endodermis

xylem vessels

Transpiration

o Definition

The loss of water vapor from the aerial parts of a plant, especially

through the stomata of the leaves

o A consequence of gaseous exchange

There are numerous mesophyll cells present within a leaf, and these

are surrounded by intercellular air spaces

Water continually moves out of the mesophyll cells to form a thin film

of moisture over their surface

From the wet cell walls, water evaporates into the intercellular spaces,

and from there it diffuses through the stomata to the drier air outside

the leaf

o Effects

Air movement

The higher the air movement, the higher the rate of

transpiration

Temperature

A rise in temperature will result in a rise in rate of evaporation

(transpiration)

Humidity of air

The more humid the air, the slower the rate of transpiration

Light intensity

High light intensity will cause stomata opening

This will increase the rate of transpiration

o Wilting

The turgor pressure in the mesophyll cells in the leaf

Supports the leaf

Keep the leaf firm and widely spread out to absorb sunlight for

photosynthesis

In strong sunlight, excessive transpiration causes the cells to lose their

turgor

They become flaccid and the plant wilts

o Translocation

Definition

The transport of manufactured substances like sugars and

amino acids in plants

Translocation of sugars and amino acids occurs in the phloem

Experiment with aphids

Ringing experiment

Use of 14C isotopes

Transport in humans

Main blood vessels

o Pulmonary artery

Heart to lungs

o Pulmonary vein

Lungs to heart

o Hepatic artery

Heart to liver

o Hepatic vein

Liver to heart

o Renal artery

Heart to kidneys

o Renal vein

Kidneys to arteries

Functions of blood

o Red blood cells

Contains hemoglobin

A red pigment

Special kind of protein containing iron

Oxygen carrier

o White blood cells

Two main kinds

Lymphocytes

o Produces antibodies

Phagocytes

o Phagocytosis

o Tissue rejection

o Platelets

Aids in the clotting of blood Fibrinogen fibrin

o Plasma

Transport medium

Blood cells

Ions

Soluble food substances

Hormones

Carbon dioxide

Urea

Vitamins

Plasma proteins

Blood groups

o Types

A

B

AB

O

o Possible combinations for the donor and recipient

O (donor) A (donor) B (donor) AB (donor)

O (recipient) √

A (recipient) √ √

B (recipient) √ √

AB (recipient) √ √ √ √

Arteries

o Arteries have walls that are thick, muscular and elastic to withstand the high

pressure of blood coming out from the heart

o Strength of an artery to resist the pressure comes largely from its elastic

fibres

o Thick elastic walls also help to maintain the high blood pressure in the artery

o Elastic layer is much thicker in arteries near the heart

o Elasticity allows the arteries to stretch and recoil, thus propelling the blood

along the blood vessel

o The constriction and dilation of an artery is brought about by the contraction

and relaxation of the muscles in the arterial walls

Veins

o Blood in veins are at a lower pressure and flows more slowly and smoothly

o The walls of veins are not as thick and muscular as those of arteries

o Veins contains less elastic tissue

o Semi-lunar valves

Folds of the inner walls in veins that aids in preventing back flow of

blood

o Prevention of back flow is important in returning the blood to the heart

o Presence of semi-lunar valves ensures unidirectional blood flow of blood

o The movement of blood along the veins is assisted by the action of the skeletal muscles on the veins muscular contractions and relaxation exert a

pressure on the veins, thus moving blood along

Capillaries

o Microscopic blood vessels found between cells of almost all tissues

o Endothelium

A single layer of flattened cells that makes up the wall of capillaries

o The endothelium is partially permeable to ensure rapid diffusion of substances

through it

o Capillaries branch repeatedly to increase surface area for exchange of

substances

o Blood pressure in capillaries is also lowered, thus blood flow is slowed down,

allowing more time for exchange of substances

Transfer of materials between capillaries and tissue cells

o High blood pressure at the arterial end of capillaries forces out blood plasma

into spaces between cells

o White blood corpuscles can also squeeze through, but no red blood corpuscles

o Tissue fluid

Diluted plasma containing white corpuscles

o Tissue fluid is a colorless liquid

o Some cells do not have direct contact with blood vessels

o However, these cells are bathed by tissue fluid

o Tissue fluid carries substances in solution between the tissue cells and the

blood capillaries

o Dissolved food substances and oxygen diffuse from the blood into the tissue

fluid and then into the cells

o Waste products diffuse from the cells into the tissue fluid and then through

the capillary walls into the blood

o As capillaries are small, erythrocytes can only move through them in single

file

Red blood cells may even become bell-shaped

o The advantages of this are

The diameter of the erythrocyte is decreased so that it can pass easily

through the lumen of the capillaries

The cell increases its surface area to speed up absorption of waste

products and release of oxygen

Rate of blood flow is reduced, giving more time for efficient gaseous

exchange

Heart

o Size is about the size of a clenched fist in man

o Lies in the thorax, behind the sternum and between the two lungs, displaced

to the left side of the body

o Conical in shape and slants with its apex directed slightly towards the left side

of the body

o Pericardium

A two-layered bag surrounding the heart

The inner membrane being in contact with the heart while the

pericardial fluid lies between the two membrane

o Made up of four chambers

Two upper atria and two lower ventricles

o Median septum

Muscular wall that separates the right chambers from the left

chambers, thus preventing mixing of oxygenated and deoxygenated

blood

o Blood is returned to the right and left from the vena cava and the pulmonary

vein respectively

o Contraction of the atria will cause the blood in the atria to be pumped into the

right and left ventricles accordingly

o Blood is pumped out of the heart by the ventricles

Pulmonary arch and pulmonary arteries carry blood to the lungs, aortic

arch carries blood to the other parts of the body

o Backflow is prevented due to the presence of valves

Tricuspid valve in the right side, bicuspid valve on the left side

Blood clotting

o Clotting of blood seals up a wound to prevent excessive loss of blood

o Clotting also prevents entry of foreign particles into the blood stream

o Hemophilia

A genetic disease where the clotting mechanism is greatly impaired,

thus hemophilics may bleed to death

o Damaged tissues and platelets thrombokinase

o Prothrombin + thrombokinase + Ca2+ thrombin

o Fribinogen + thrombin insoluble fibrin threads

o When blood vessels are damaged, an enzyme (thrombokinase) is released by

the damaged tissues and blood platelets

o Thrombokinase converts the protein prothrombin normally present in the

plasma to thrombin, which is an enzyme

o Calcium ions are required for the conversion of prothrombin to thrombin

o Thrombin catalyzes the conversion of the soluble protein fibrinogen to a

meshwork of insoluble threads of fibrin

o Fibrin threads entangle blood corpuscles and the whole mass forms a clot

o Vitamin K is also essential for the process of blood clotting

o In undamaged blood vessels, the blood does not clot due to the presence of

heparin, an anti-clotting substance produced by the liver

o During blood clot, thrombokinase released neutralizes the action of heparin so

that clotting can take place

o When blood clots, serum is left behind

o Serum

A yellowish liquid that has the same composition as plasma except

that it lacks the clotting constituents

Cardiac cycle

o Contraction of the atria will cause the blood in the atria to be pumped into the

right and left ventricles accordingly

o Ventricular contraction is also known as ventricular systole (producing ‘lubb’

sound due to the closing of the tricuspid and bicuspid valves)

o Semi-lunar valves are present to prevent back flow of blood into the

ventricles

o Ventricular relaxation is also known as ventricular diastole (producing the

‘dubb’ sound due to the closing of the semi-lunar valves)

o A systole and a diastole makes up one heartbeat

o The rate of heartbeat varies between people

Coronary heart disease

o Two coronary arteries bring oxygen to the cardiac muscles

o Obstruction to blood flow in these two arteries may bring about cardiac arrest

or angina pectoris

o Coronary thrombosis

Formation of blood clot in the artery

o If thrombosis occurs in the coronary arteries, blood is prevented from

reaching the heart cardiac arrest

o Heart attack/heart failure

Sudden slowing or stoppages of the heartbeat due to severe damage

or death of cardiac muscles

o Coronary thrombosis is more likely to occur in narrow arteries with fatty

deposits

o Atherosclerosis

The narrowing and hardening of artery due to fatty deposits on the

walls of the artery

o Walls of artery with atherosclerosis are thick and hard, with the rough inner

surfaces increasing the risk of thrombosis

o What happens leading up to coronary heart disease

Cholesterol and polysaturated fats are deposited on the walls of the

artery, narrowing and hardening the artery

As the narrowing of lumen would result in rougher inner surfaces, a

blood clot is likely to be formed

The blood clot would inhibit the blood from reaching the heart and

cause heart attacks or heart failure

o Coronary heart disease can be caused by

Diet

Diet rich in cholesterol and saturated animal fats results in high

blood cholesterol level

Lack of exercise/being overweight

Stress

Hormone adrenaline secreted under stress conditions increases

heart beat rate and blood pressure

Drinking

Smoking

Nicotine

o Increases the rate of heart beat by increasing secretion

of the hormone adrenaline

o Causes the blood vessels to constrict, increasing the

blood pressure

o Causes blood to clot more easily

Carbon monoxide

o Increases the rate of fatty deposition on inner surfaces

of the arteries and decreases oxygen supply to the heart

o Preventive measures can be taken as atherosclerosis begins early in life

Avoid diets rich in saturated animal fats

Substitute with polyunsaturated vegetable fats

Regular exercising

o Strengthens the heart and maintains elasticity of the

arterial walls

Minimal or no smoking and drinking

Low-stress lifestyle or proper stress management

Respiration

Alveoli

o The walls of the alveoli are the respiratory surfaces, and these are one cell-

thick

o Numerous capillaries are closely wrapped around outside of the alveoli

o Oxygen can diffuse across the walls of the alveoli into the blood

o Carbon dioxide can diffuse the other way

Removal of carbon dioxide from the lungs

o Blood entering the lungs is rich in carbon dioxide in the form of hydrogen

carbonate ions H2O + CO2 H2CO3 H+ + HCO3

-

o This is also a reversible reaction

o As tissue cells respire, carbon dioxide is evolved

o Carbon dioxide diffuses into the blood and dissolves in the water in the red

blood cells to form carbonic acid

o This reaction is catalyzed by the enzyme carbonic anhydrase

o Carbonic acid is converted to hydrogen carbonates in the red blood cells

o Much of hydrogen carbonates formed will diffuse back into the plasma

o Thus, hydrogen carbonates are carried both in the red blood cells as well as in

the plasma

o When blood passes through the lungs, alveolar carbon dioxide concentration

is low

o Carbonic anhydrase will catalyze the backward reaction and hydrogen

carbonates are converted to water and carbon dioxide in the red blood cells

o Carbon dioxide will diffuse out of the blood in the alveoli to be exhaled out to

the external environment

o Some moisture and heat will also be exhaled out in this manner

Cilia

o Cilia are hair-like structures which lines the trachea, moves to and fro in a

wave-like rhythm to sweep the ‘dirty’ mucus up the larynx and into the

pharynx to be swallowed down the esophagus

Diaphragm

o To increase volume of the thorax during inspiration (inhalation)

o To decrease volume of the thorax during expiration (exhalation)

Ribs

o Ribs are pulled upwards and outwards during inspiration (inhalation) to

increase volume of the thorax

o Ribs are dropped to its normal position during expiration (exhalation) to

decrease volume of the thorax

Intercostal muscles

o During inspiration (inhalation), the external intercostal muscles contract,

while the internal intercostal muscles relax, pulling the rib cage upwards and

outwards, and pulling sternum upward and forward

o This is done to increase volume of the thorax

o During expiration (exhalation), the external intercostal muscles relax, while

the internal intercostal muscles contract, causing the rib cage to drop again to

its normal position

o This is done to decrease volume of the thorax

Effects of tobacco smoke

o Cigarette smoke contains more than 4000 chemicals, many of which are

carcinogenic

o Smoking can cause harmful diseases in man

o Chemicals in tobacco smoke

Nicotine

Carbon monoxide

Tar

o Effects of nicotine on the body

Increase in heartbeat and blood pressure

Increased risk of blood clots in arteries

o Effects of carbon monoxide on the body

Death

Increased risk of atherosclerosis

Increased risk of blood clots in arteries

o Effects of tar on the body

Blockage in alveoli reduces gas exchange efficiency

Mucus cannot be removed

Increase risk of chronic bronchitis

Increased risk of emphysema

Aerobic respiration

o The breakdown of food substances in the presence of oxygen with the release

of a large amount of energy

o Word equation Glucose + oxygen carbon dioxide + water + energy

o Chemical equation C6H12O6 + O2 CO2 + H2O (38 ATP)

Anaerobic respiration

o The breakdown of food substances with the release of a comparatively small

amount of energy in the absence of oxygen

o Word equation Glucose carbon dioxide + ethanol + energy

o Chemical equation C6H12O6 2CO2 + 2C2H5OH (2 ATP)

Effects of lactic acid on muscles

o This will cause muscle fatigue and the body will need to rest to recover

Excretion

The process by which metabolic waste products are removed from the body of an

organism

Importance of removing nitrogenous and other compounds

o Ensure that chemical reactions proceed in the correct direction

o Certain metabolic wastes are toxic

Ultrafiltration

o Blood from the renal artery brings metabolic wastes and useful substances to

the kidney tubules

o Most of the blood plasma is forced out of the glomercular blood capillaries into

the Bowman’s capsule

o Is the process of small molecules being forced into the nephron due to high

blood pressure

o Factors of ultrafiltration

Hydrostatic blood pressure

Blood pressure in the glomerulus is high because the efferent

arteriole is narrower than the afferent arteriole, hence providing

the main force required for filtrate to leak through the porous

capillary wall of glomerulus

Partially permeable membrane

Allowing only small molecules to diffuse across

o Filtrate

Glucose, vitamins, amino acids, hormones, bicarbonate ions, mineral

salts and other nitrogenous waste products

o Remnants

Blood cells and all large molecules like blood platelets, blood

corpuscles, proteins and fats

o The filtrate trickles down into the proximal convoluted tubule, the loop of

Henlé and then to the distal convoluted tubule, then down into the collecting

duct

Selective reabsorption

o About 120cm3 of filtrate are formed in the kidney every minute

There is a need to reabsorb useful materials

Selective reabsorption takes place to take back useful materials

o At the proximal convoluted tubule, mineral salts, glucose, amino acids, and

other useful substances are reabsorbed through the walls of the tubules into

the blood capillaries through active transport and diffusion

o Highly selective

Receptors only pumps in those that are needed by the body

o The large molecules that remain in the blood capillaries act osmotically to

reabsorb water in the tubule

o Most of the water is reabsorbed mainly by osmosis

o Some of the water is reabsorbed in the loop of Henlé, distal convoluted tubule

and collecting duct into the surrounding blood capillaries

o Some salts are also reabsorbed from the distal convoluted tubule

o Excess water, mineral salts and nitrogenous waste products are allowed to

pass through along the uriniferous tube and out through the collecting tubule

into the renal pelvis and into the ureter as urine

o Blood that flows away from the kidney tubule contains very little urea and

less excess water

o The fluid in the nephron flows in one direction while the capillaries flow in the

opposite direction

o This is known as countercurrent flow

o Countercurrent flow occurs to allow for maximum reabsorption of substances

o Most water is reabsorbed by diffusion, followed by osmosis according to the

control of the anti-diuretic hormone (ADH) made in the hypothalamus of the

brain

o ADH is stored in the pituitary gland of brain

o The osmoreceptors in the hypothalamus of the brain monitors the osmotic

pressure of the blood passing through

o If the osmotic pressure of the blood rises, more ADH released from the

pituitary will increase the permeability of the tubule wall and more water will

be reabsorbed, hence less urine will be formed

o The production of a large quantity of water urine is known as diuresis

o ADH serves to counter this condition, and thus the name

Kidney dialysis

o An artery is joined to a vein, creating a arteriovenous fistula

o Blood is then drawn from the vein in the arm of a patient and allowed to flow

through the dialysis tubing in the machine

o This tubing is narrow, long and coiled to increase surface area

o Its walls are selectively permeable

o The dialysis tubing is bathed in a dialysis liquid similar to blood plasma

o Small molecules that are waste products like urea diffuse out of the tubing

into the dialysis liquid

o Big particles like blood cells and plasma protein remain in the tubing

o The blood is not only cleansed but the amount of salt and water is adjusted

before it is returned to the patient

o The “cleansed” blood is returned to the patient through a tube connected to a

vein in the arm

o Countercurrent flow is observed to maintain concentration gradient

Homeostasis

Definition

o The maintenance of a constant internal environment

Process of homeostasis

o A change in the internal environment (stimulus)

o A corrective mechanism

o A negative feedback

o In general, if some factor becomes excessive or too little, a control system

initiates a feedback mechanism, which consists of a series of changes that

return the factor toward a certain mean value, thus maintaining homeostasis

o Negative feedback serves to prevent the self-regulatory corrective mechanism

from over-compensation

Maintenance of body temperature

o Insulation

The thicker one’s skin is, the higher the insulation, thus he or she

loses or gains heat at a slower rate

o Temperature receptors in the skin

The temperature receptors in the skin sense changes in the

environment and transmit a signal to the hypothalamus to start the

corrective mechanism to effect a change

o Sweating

Another characteristics of mammals

Each sweat glands is a coiled tube formed by a down-growth of the

epidermis

It forms a tight knot in the dermis and is richly surrounded by blood

capillaries

These secrete a liquid called sweat

Sweat is mostly water, with small amounts of salt and urea dissolved

in it

It travels up the sweat ducts, and out onto the surface of the skin

through the sweat pores

Sweat is secreted continuously but sometimes in very small quantities

which evaporate almost immediately

Sweat helps in temperature regulation (removal of latent heat)

o Shivering

A very fast random contraction and relaxation of muscles, which

generates heat to warm the blood

o Blood vessels near the skin surface

When one is too warm

Vasodilation is brought about

o More blood is brought to the surface of the skin and

more heat is lost through radiation, conduction and

convention

Constriction of shunt vessels to allow more blood to be brought

to the surface

When one is too cold

Vasoconstriction is brought about

o This prevents blood from flowing to the surface of the

skin

o Instead it has to go through the capillaries which lie

below the fat layer

o This reduces the amount of heat lost by radiation from

the blood to the air

Dilation of shunt vessels to direct blood away from the surface

o Coordinating role of brain

The hypothalamus in the brain is responsible to prevent over-

compensation

In other words, the brain controls when compensation is to be ceased

Co-ordination and response

Relationship between receptors, central nervous system and effectors

o The receptors send impulses to the central nervous systems, which transmits

another impulse to the effectors, which response to the stimuli

Structure of the eye

o Cornea

Dome-shaped transparent layer continuous with the sclera

Specialized form of conjunctiva

Refracts light rays into the eye

Causes most of the refraction of light

o Iris

Circular sheet of muscles that controls the amount of light into the eye

Pigmented to give the eye its color (it may vary from blue to grey or

green to brown)

Two sets of involuntary muscles present

Circular muscles and radial muscles

o Pupil

Hole in the centre of the iris

Allows light to enter into the eye

o Sclera

Outermost layer, tough, white, fibrous coat

Forms a protective layer round the eyeball and continues as a

transparent cornea which forms a small bulge at the front of the eye

Cornea

Transparent part of the sclera

The cornea allows light to enter

The cornea is denser than the air medium, thus light rays falling onto

it are refracted inwards towards the lens

o Conjunctiva

A thin transparent membrane covering the exposed part of the eyeball

It is a mucous membrane that secretes mucus to keep the eye moist

The conjunctiva is continuous with the skin of the eyelids

o Eyelids

Serve to protect the eyeball against mechanical injury

Act as a shutter and help control the amount of light intensity entering

the light

o Lachrymal gland

Secretes tears to lubricate the conjunctiva

The tear gland lies in the outer corner of the upper eyelid

Tears flow between the eyelids and the exposed part of the eyeball,

helping to reduce friction when the eyelids move

Dust particles entering the eyes will cause a great production of tears

to wash them away

Tears contain an enzyme called lysozyme, which can kill bacteria

Blinking spreads tears over the cornea and conjunctiva and wipes dust

particles off the cornea

o Naso-lachrymal duct

Duct where excess tear drains into

The naso-lachrymal duct runs from the inner corner of the eye to the

nose

Emotion may cause excess tears to be secreted and passed into the

naso-lachrymal duct

o Eyelashes

Help to shield the eye from dust particles

o Choroid coat

The middle layer of the eyeball

Contains a network of blood capillaries that nourishes the eye as well

as removes waste

Pigmented black to prevent internal reflection of light

Anterior end of the choroid is modified to form the ciliary body and the

iris

Ciliary body

Thickened region at the front end of the choroids that contains

many involuntary circular muscles called ciliary muscles

Intrinsic eye muscles since they are inside the eyeball

Ciliary muscles control the curvature or the thickness of the

lens

Ciliary muscles pay an important part in focusing and

accommodation

Iris

Circular sheet of muscles with a round hold in the centre

Pupil

The central hole in the iris which allows light to pass into the

eye

Lens

Transparent, elastic, biconvex crystalline lens

Situated behind the iris and in contact with the iris

The lens is attached to the ciliary body by the suspensory

ligaments

Divides the eyeball into two chambers

o The small chamber in front of the iris and the lens is

filled with a water fluid known as aqueous humour

o The larger chamber behind the lens is filled with a

transparent jelly-like fluid, the vitreous humour

Both aqueous humour and vitreous humour serve to keep the

eyeball firm and to refract light

o Retina

Innermost layer of the eyeball

Light-sensitive layer on which images are formed

Presence of photoreceptors

Rods and cones

These cells are connected to the nerve-endings from the optic nerve

o Rods

Contains visual purple

The pigment concerned with vision in dim light

Light causes bleaching of visual purple which is involved in light

detection

In bright light, all the visual purple is bleached

It takes a short time for visual purple to be formed again in the rods

Thus, when a person enters a dark place from a bright one, he may

not be able to distinguish the objects around him for some time

Formation of visual purple requires Vitamin A

A person with deficiency in Vitamin A may not be able to see in dim

light, a condition known as night-blindness

Rods are sensitive to dim light, but only let one see in black and white

o Cones

Less sensitive than rods, thus it is inefficient in dim light

Concerned with bright light and color vision

Three types of cones, each possessing a different pigment

Red, green and blue

Thus, cones enable one to see light at different colors

Fovea centralis (yellow spot)

A shallow yellow depression in the retina in line with or on the

optical axis of the lens

Place where images are normally focused

Contains only cones

Thus vision is keenest in bright light when images are focused

onto the yellow spot

Optic nerve

Nerve that transmit impulses to the brain when the

photoreceptors are stimulated

Blind spot

On the retina immediately over the optic nerve

Absences of any photoreceptors, thus this area is insensitive to

light

Accommodation for near objects

o Light rays from a near object are diverging

o Refraction by cornea and aqueous humour into the pupil

o Contraction of the ciliary muscles

o Pull on the suspensory ligaments is released o Lens becomes thicker and more convex contracted

o Light rays from near objects are sharply focused on the retina

o Photoreceptors stimulated

o Nerve impulses transmitted to brain via the optic nerve

o Brain interprets the impulses and near object is seen

o The nearer the objects, the more the circular muscles will contract and the

thicker the lens will be

o Near point

Point where the object is so close to the eye that in order to see it, the

ciliary muscle must contract fully and the lens become most convex

If the object is moved nearer to the eye, the image formed on the

retina will be blurred as the lens cannot adjust any further

Accommodation for a distant vision (≥7m)

o For a distant object, the light rays are almost parallel to each other when they

reach the eye

o Parallel rays are refracted by cornea and aqueous humour into the pupil

o Relaxation of ciliary mscles o Pull on suspensory ligaments increase becomes taut, pulling on the edge of

the elastic lens

o The lens become flatter and less convex relax

o Light rays from the distant object are sharply focused on the retina

o Photoreceptors stimulated

o Nerve impulses transmitted to brain via the optic nerve

o Brain interprets the impulses and far object is seen

Light and pupil reflex

o The size of the pupil changes to allow a suitable amount of light to pass into

the eye

This protects the inner layer of the eye from damage

And in dim light, allows more light to enter the eye in order to see

clearly

o The size of the pupil is controlled by two sets of involuntary muscles in the iris

Circular muscles and radial muscles

o When the circular muscles contract, the radial muscles relax pupil becomes

smaller o When the circular muscles relax, the radial muscles contract pupil becomes

larger

o Thus, the size of the pupil will control the amount of light entering the eye

o The pupil becomes smaller in light of high intensity

o The pupil becomes larger in low light intensity

o This is a reflex action

Contraction and relaxation of these involuntary muscles are automatic

and immediate in response to the stimulus of light

o Sometimes, the light intensity is so bright that decreasing the size of the pupil

is not enough

o The eyelids have to come closer together to screen off part of the light

o The pupil reflex arc Stimulus (change in light intensity) receptor (retina) sensory

neurone in optic nerve brain motor neurone effector (iris)

Nervous system

o Function

Co-ordinate and regulate bodily functions

Sensory neurons

o Afferent/receptor neurons

o Transmit impulses from the receptors to the central nervous system

Relaying neurons

o Intermediate neurons

o Transmit impulses from the afferent neurons to the efferent neurons and are

found within the central nervous system

Efferent neurons

o Motor/effector neurons

o Transmit impulses from the central nervous system to the effectors

Reflex actions

o The nervous pathway for reflex action is the reflex arc

o A stimuli stimulates the nerve endings (receptor/sense organ) in the skin

o Impulses are produced

These travel along the sensory neurone to the spinal cord or the brain

o In the spinal cord or the brain (reflex centre), the impulses are transmitted

first across a synapse to the intermediate or relaying neurone, and then

across another synapse to the motor neurone (an impulse may also be

transmitted to the brain at the same time)

o Motor impulses leave the spinal cord along the motor neurone to the effector

o The effector (muscles or glands) brings about a respond to the stimuli

Hormone

o Chemical substances produced in minute quantities by certain parts of the

body and transported in the bloodstream to other parts where they exert an

effect

Endocrine gland

o Glands without ducts or glands of internal secretions

o The islets of Langerhans in the pancreas secrete the hormone insulin into the

blood stream

Adrenaline

o It increases the rate of conversion of glycogen to glucose in the liver, thus

increasing blood sugar level so that more glucose is available for energy

production

o Stimulus includes fear, anger, anxiety or stress

Insulin

o Stimulates absorption of glucose by cells so that they can break it down to

release energy

o Directing the conversion of excess glucose to glycogen for storage in liver or

muscles

o Increasing oxidation of glucose during tissue respiration

o Thus, decreasing blood glucose concentration

Glucagon

o Conversion of glycogen into glucose

o Conversion of fats and amino acids into glucose

o Conversion of lactic acid into glucose

o Thus, increasing blood glucose concentration

Diabetes mellitus

o Symptoms

High blood glucose level

Lack of secretion of insulin, the body cannot use or store

glucose

This brings about a rise in blood glucose concentration

Glucose in urine

As insulin is not secreted, blood glucose is not reabsorbed by

the body and is lost in the urine

o Treatment

People with Type 1 diabetes have to inject insulin into their bodies

daily.

They also need to ensure that they have a ready supply of sugary food

as their blood glucose concentration can drop drastically (either from

over-dosage of insulin, exercising too much or eating too little)

People with Type 2 diabetes need to control their blood glucose

concentration by regulating intake of carbohydrates in their diet and

by regular exercising

If lifestyle changes fail, then the patients may need to take medication

(e.g. metformin tablets) or insulin injection